Octave and atlas.

[Douglas Eck]

I'm cc'ing the octave community on this note to Dirk Eddlbuettel
because his advice was very helpful to me. This info will be
obvious to many of you, but perhaps not to all. 

I wrote to Dirk E. about octave / atlas support and he let me know
that it's already in the Debian woody dist (which I use). He suggested
that I could rebuild atlas for my machine architecture (Athelon) 
and perhaps see an additional speedup.

The speedup from the rebuild was dramatic. Previously I had been
running atlas libs built around an Intel PIII. Now I'm running
with libs built for my athelon.  The following (granted, not very thorough)
simple test program runs Šþ=50% faster with the Athelon libs than with 
the PIII libs. (Ok, 50% is optimistic overall, but for matrix multiplication
it seems to hold)
  
function [] = testexp()
  a=rand(10,10);
  b=rand(100,100);
  c=rand(100,100);
  tic
  for i=1:10000
    exp(a);
    d=b*c;
  end
  toc

I just thought I'd pass that on, in case it wasn't obvious to 
everyone: it may be worth the time to rebuild atlas around
your specific processor. 

FYI. On my 800Mhz Athelon with 256MB Ram, that testexp()
program now executes in Šþ=16 seconds using Octave 2.1.32.
It took Šþ=25 seconds using the PIII libs.

It takes Šþ=55 seconds in Matlab 5.3.1 for linux!
Octave is >3 times faster in this instance. 

Cheers,
Doug



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